But tuples (and cells) are mutable in pure CPython if you believe strongly enough.

See: https://gist.github.com/llllllllll/b1ac68a6b77535a64c0b13bfd... https://gist.github.com/dutc/d2ff9f17a0520d233b2d197d1dafa1a... https://twitter.com/__qualname__/status/867928378040438784